Preheat oven to 350°F. Set aside a large loaf pan (6 ½ x 10 inches) or a similar-sized pan.
To a medium skillet over medium heat, add vegetable oil. Once hot, add the onion and green bell pepper, sautéing until softened, about 4-5 minutes.
Add minced garlic and cook for an additional minute. Remove from the heat and let cool slightly.
In a large bowl, combine the cooled vegetables, ground beef, ground pork, eggs, pinto beans, breadcrumbs, ½ cup of the BBQ sauce, Worcestershire sauce, chili powder, salt, cayenne, and black pepper. Mix gently but thoroughly until just combined. Avoid overmixing to keep the meatloaf from becoming tough.
Press half of the meat mixture into the prepared loaf pan, creating an even layer. Using the back of a spoon, make a shallow indentation in the center of this layer.
Sprinkle the shredded cheddar cheese evenly within the indentation. Top with the remaining meat mixture, pressing gently to seal the cheese inside. Form into a loaf.
Brush ¼ cup of the remaining BBQ sauce over the top of the meatloaf, reserving the rest of the BBQ sauce for later.
Bake for 40 minutes. Carefully remove from the oven and brush with the remaining BBQ sauce.
Return the meatloaf to the oven and bake for an additional 25-30 minutes, or until the internal temperature reaches 160°F (71°C) on a meat thermometer.
Allow the meatloaf to rest for 5 minutes before slicing and serving.